a. robertson, 2006 © science of aflatoxin growth and identification alison robertson extension...
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A. Robertson, 2006 ©
Science of Science of
aflatoxin growth and identificationaflatoxin growth and identification
Alison RobertsonExtension Field Crops Pathologist
A. Robertson, 2006 ©
What is aflatoxin?
Poisonous substance produced by the fungi Aspergillus flavus and A. parasiticus.
- once produced, they are VERY stable
Production of toxins highly variable:
• fungal strain and species• storage temperature + moisture content• length and type of storage• other unknown factors
A. Robertson, 2006 ©
Therefore mold ≠ aflatoxins
Usually thought of as a storage pathogen
BUT
fungal contaminations starts in the field
Life Cycle of
Aspergillus flavus
A. Robertson, 2006 ©
Survives as conidia and sclerotia
in soil and crop debris
Wind and insects
Population dynamics of A. flavusShearer et al., 1992; McGee et al. 1996
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Populations measured once a month
Populations in soil significantly greater in
July vs June, Aug & Sept
1992 & 1993 - A. flavus recovered at greater frequencies in CC and no till
Through the silks:Yellow/brown = germination and colonization
Pollination = changes in physiology and structure of silk
A. flavus continues growth as a saprophyte
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Aspergillus : Disease cycle
1. Infection
Enhanced by damage by birds/insects
Physical damage allows further spread
Broken pericarp allows invasion
Moisture content drops rapidly <35%
A. flavus competes successfully with other MOs (e.g. Fusarium spp.)
grows best at 17-20% grain moisture
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2. Colonization
High max, min and ambient temp (esp. July and Aug) – particularly night – more important than
moisture
Very low rainfall
Stressed plants = altered nutritional status of developing kernels
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3. Colonization and aflatoxin production
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Optimum conditions for Aspergillus growth and aflatoxin production
Temperature
Moisture
13% 30%
45F 120FAspergillus growth
Aflatoxin production17%
55F 104F
? %
So, the fungus can grow at higher and lower temperatures & moistures and not produce aflatoxin
Managing Aspergillus and aflatoxin
1. Early planting (April v May)
2. Reduce plant stress
3. Harvest early
4. Avoid damage during harvest
5. Dry grain a.s.a.p. to 13% moisture (inhibits growth at any temperature)
6. Cool grain a.s.a.p. to <45F (very slow growth <55F)
7. Ensure storage facilities are clean
A. Robertson, 2006 ©
A. Robertson, 2006 ©
Identification
2. Aflatoxins
a.Black light
# BGYF particles ≠ aflatoxin = false positive
The black light should no longer be used for any type of mycotoxin screening
http://archive.gipsa.usda.gov/pubs/mycobook.pdf
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b.Test kits
- immunoassay strips
- ELISA assays
- detect +/- 20ppb
USDA GIPSA approved list://151.121.3.117/techservsup/metheqp/testkit.htm
c.HPLC
- quantitative
- list of labs
www.iowagrain.org
(detection)
(identification)
References
Diener et al. 1987. Ann. Rev. Phytopathol. 25: 249-70
Jones et al. 1980. Plant Disease 64: 859-863
Jones et al. 1981. Phytopathology 71: 810-816
Marsh and Payne. 1984. Phytopathology 74: 1284-1289
Schindeer et al. 1967. Applied Microbiology 15: 1006-1009
Wicklow and Donahue. 1984. Trans. Br. Mycol. Soc. 82: 621-624
Aflatoxins in Corn. Pm1800. Iowa State University Extension
Aflatoxin in Corn. http://aes.missouri.edu/delta/croppest/aflacorn.stm